Jerrold Jones walks his dog Buddy near the Yosemite Slough, located between Candlestick Park and the Shipyard March 27, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

The Yosemite Slough, located between Candlestick Park and the Shipyard March 28, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

The Yosemite Slough, located between Candlestick Park and the Shipyard March 28, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

An old tire is visible at the Yosemite Slough at low tide, located between Candlestick Park and the Shipyard March 27, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

Ann Meneguzzi, supervising ranger Candlestick point, is seen at the the Yosemite Slough wetlands restoration project on Tuesday, November 22, 2011 in San Francisco.

Photo: Lea Suzuki, The Chronicle

Ann Meneguzzi, supervising ranger Candlestick point, is seen at the...

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The Yosemite Slough, located between Candlestick Park and the Shipyard March 28, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

Dumpsters over flowing with debris that was collected along Yosemite Slough near Candlestick Park in San Francisco, Calif. on Saturday Sept. 20, 2008. Much of the debris was from homeless encampments along the waterway. Marisa Deutsch tosses trash into the bin, during the statewide 2008 Beach Cleanup Day.

Photo: Michael Macor, The Chronicle

Dumpsters over flowing with debris that was collected along...

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Water laps the shore around a discarded shirt at the Yosemite Slough, located between Candlestick Park and the Shipyard March 28, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

The Yosemite Slough at low tide, located between Candlestick Park and the Shipyard March 27, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

The Yosemite Slough, located between Candlestick Park and the Shipyard March 28, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

The Yosemite Slough at low tide, located between Candlestick Park and the Shipyard March 27, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

Part of an old bottle is visible at the Yosemite Slough at low tide, located between Candlestick Park and the Shipyard March 27, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

Water laps the shore, littered with tiny dead crabs and garbage at the Yosemite Slough, located between Candlestick Park and the Shipyard March 28, 2014 in San Francisco, Calif. The EPA will be posting signs around the area in the coming weeks warning the public against fishing, wading or swimming in the Slough due to contamination.

Volunteer Dede Hapner applies a fresh coat of paint to a wall near Yosemite Slough during the annual Earth Day clean-up at Candlestick Point State Recreation Area in San Francisco, Calif. on Saturday, April 14, 2012.

Photo: Paul Chinn, The Chronicle

Volunteer Dede Hapner applies a fresh coat of paint to a wall near...

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A newly constructed bird island providing a potential nesting site for local and migratory birds is seen surrounded by water at the Yosemite Slough wetlands restoration project on Tuesday, November 22, 2011 in San Francisco.

Photo: Lea Suzuki, The Chronicle

A newly constructed bird island providing a potential nesting site...

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Two volunteers pick up debris from the shoreline of Yosemite Slough during the annual coastal cleanup near Candlestick Park in San Francisco, Calif. on Saturday, Sept. 17, 2011.

Photo: Paul Chinn, The Chronicle

Two volunteers pick up debris from the shoreline of Yosemite Slough...

After years of cleaning up surrounding areas, federal regulators say they will tackle the extensive contamination in Yosemite Slough, the intertidal channel between Candlestick Point and the Hunters Point Shipyard.

In the coming weeks, the U.S. Environmental Protection Agency will post signs warning the public that lead and PCBs pollute the mud there and threaten the health of people and wildlife. In the coming years, the agency will undertake a $15 million cleanup that will involve removing an estimated 1,100 truckloads of contaminated soil from the top 2 to 3 feet of the marine area and capping it with clean sand.

While the slough is mostly fenced off and technically off-limits to the public, EPA regional Administrator Jared Blumenfeld said it is frequented by fishermen and people digging for shellfish, as well as illegal dumpers and copper thieves, who load boats at high tide. The top layer of mud has an average of 5,000 parts per billion of PCB contamination, according to the agency. An average of 386 parts per billion is considered safe for humans and the environment.

"It should be very, very clear that you can't swim, fish or go in the water there, and it isn't," Blumenfeld said. "It's been contaminated for a long time. The levels of PCBs are very high ... but everybody has spent the majority of their time on the shipyard and Candlestick. This is sandwiched in between and is in desperate need of cleanup."

The EPA will pay for the cleanup by pursuing money from dozens of companies it has determined are in part responsible for the contamination at the site, Blumenfeld said. That settlement process should be completed by the end of the year.

History of the slough

The slough was once part of a larger natural marine estuary in the area, according to the EPA, but was narrowed during the 1940s, '50s and '60s when construction debris, crushed rock and other waste was dumped there. Now, the narrow slough runs up against the industrial area of the Bayview district and is surrounded by green fields to the north and private properties west and south.

At low tide, marshy mudflats lead out to the sparkling bay; at high tide, the area is covered by 3 to 6 feet of water. It is fenced off, but easy to get into: On the north side, near Van Dyke Avenue, there's a gaping opening that offers easy pedestrian access to the banks of the slough.

The EPA says the contamination is the result of industrial waste dumping as well as years of sewer and storm water discharge. Improvements to the city's sewer system have reduced wastewater discharges to about once a year during heavy rains, but Blumenfeld said dumping continues.

The contamination can have serious impacts on people and animals that come into direct contact with the mud, according to the EPA.

PCBs, or polychlorinated biphenyls, are a syntheticchemical compound widely used in fluids in electrical equipment and other machinery until a ban by Congress in 1979 because of toxicity levels and a tendency to accumulate in the food chain.

Lead, a heavy metal that is toxic to people and wildlife, is particularly dangerous for children because it interferes with nervous system development. The lead contamination is largely the result of products that are now banned, such as lead-based paint and leaded gasoline.

Cleanup sought for years

Arc Ecology, a Bayview nonprofit that conducts environmental research and helps communities deal with pollution, has been pushing for warning signs and cleanup of the slough for years, said Executive Director Saul Bloom. Bloom said his organization, along with state and local officials, has been studying the area for more than a decade, but no agency has taken responsibility for cleanup until now.

The signs, he said - which will include warnings against wading, fishing and swimming in five languages as well as contact information for the EPA and Arc Ecology - are an important first step.

"There's been knowledge of contamination of the site for ages ... and discussions about it for ages, but nobody has done anything before now," Bloom said. "People don't think about it, even though they go there. We have pictures of people fishing there. Every time you go out there you find lures, or people camping alongside it. And we know kids from Alice Griffith Public Housing play in the slough - where would you play if you lived there?

"It's a wonderful area, but it's a neglected, poor community - and it's the industrial armpit of San Francisco in many respects."

It also feels like a throwback to a previous era, said Blumenfeld, citing the transformers and oil drums that can peek out of the mud.

"It's one of those places in San Francisco that when you are there you'd never imagine you are in San Francisco," he said. "It's like a den of iniquity. When you are there you feel like you could be in the 1850s."

Blumenfeld said the cleanup work will begin in 2017. Then the state parks agency, which owns the land, will help restore the wetlands and install a walking trail and other park amenities.